Here’s another: We have fish living right now in the Santa Cruz River.

They’re just fish someone dropped into the river, since the Santa Cruz long ago stopped being able to sustain native populations.

What’s important is that they’re living. This means we’re closer to the potential of bringing back native species that were threatened or endangered when the natural flows in the Santa Cruz River long ago ceased.

The key to this potential recovery lies in the overhaul of Pima County’s two largest wastewater reclamation plants - the largest and most complex project this county has ever undertaken.

With the project at substantial completion, there are many things to celebrate.

It came in far under budget. Originally budgeted at $720 million, effective management and strong market timing shaved $114 million off the total cost.

It is a strong example of the county’s ongoing partnership with the private market, with the county contracting with a private firm to design, build and operate one of the two recently upgraded reclamation plants.

Sewer rates, which are paying back the costs of the upgrade, remain in the mid-range for utilities nationally and will not go up this year.

And it is accomplishing what we set out to do in the first place: Meeting stringent state and federal water quality standards and providing sufficient capacity to serve this community for many years to come.

The effluent that is leaving the treatment plant meets the highest possible reuse grade, clean enough to support a fish population.

The Santa Cruz wasn’t always dry.

When aquatic biologist Frederic Morton Chamberlain came to study Arizona fishes in 1904, he found eight fish species in Pima County. Before the boom of population and urbanization, Pima County had an extensive aquatic habitat.

Chamberlain caught five different species of native fish – the longfin dace, the Gila chub, the Gila topminnow, the Sonora sucker and the desert sucker – in two different locations on the Santa Cruz, at San Xavier and at a site two miles south of Tucson. The last known records of fish along this watercourse are from 1943.

Now, with the Tres Ríos and Agua Nueva reclamation plants producing high-quality effluent flows, there is a potential that native fish species could be re-established in the region.

Why would this matter? From an ecological perspective, native fish help support other species. From a practical standpoint, they can help control mosquitoes; they have the ability to adapt to extreme cycles of flooding and drying; and they are able to live in occasional, small pools.

It’s early. Planning and study may determine this is not the best plan for the species or the community. But in a dry desert region, it’s an intriguing discussion that few anticipated could be reality.